<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        let a = 1
        let b = 2
        let c = "xx"
        let d = "yy"

        //加法
        let sum = a + b
        console.log("a+b= ", sum)
        let stringSum = c + d
        console.log("stringSum : ",stringSum)

        let test = a + c
        console.log("test is ", test)
        //test  类型为string
        console.log("typeof",typeof(test))
        // 减法
        let sub = a - b;
        console.log("sub:",sub)
        //乘法或除法
        let s1 = a * b;
        let s2 = a / b;
        console.log(s1)
        console.log(s2)
        a = a+1
        a += 1
        console.log(a)
    </script>
</head>
<body>

</body>
</html>